Rotary converter.



L. W. CHUBB.

ROTARY CONVERTER.

APPLICATION FILED JULY 6, 1915.

1,257,977. Patented Mar. 5, 1918.

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WITNESES INVENTOR law/l; WK/wbb L. w. cause. ROTARY CONVERTER. APPLICATION FILED JULY 5. 1915.

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Wn'uzsszs: 20 28 INVENTOR Aew/IsIKC/lubb L. W. CHUBB.

ROTARY CONVERTER.

I APPLICATION FI LED JULY 6, 1915. 1,257,977. Patented Mar. 5,1918.

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WITNESSES:

INVENTOR A m Z6" Lew/l5 l BY ATII'ORNEY L. W. CHUBB.

ROTARY CONVERTER.

APPLICATION mm JULY 0.191s.

Patented Mar. 5,1918. L9 5 SHEETS-SHEET 5.

53 43 45 36 as 47 49 59 54 e1 63 WITNESSES: INVENTOR i 5 fi 5g law/Ls W Ombb L. W. CHUBB. ROTARY CONVERTER. APPUCATI'ON FILED JULY 6, I915- 1,257,977. Patented Mar. 5, 1918.

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' I/r/Htl/arkroam 003 fa r /s /0 50 5 l0 l5 09/201701); m/d cai/ WITNESSES INVENTOR fim an; W all/M r BY - t E ZII7AU'QRNEY UNITED sTATEs PATENT oEEIoE.

LEWIS W. CHUBB, OF EDGEWOOD PARK, PENNSYLVANIA, ASSIGNOR TO WESTINGHOUSE ELECTRIC AND MANUFACTURING COMPANY, A CORPORATION OF PENNSYLVANIA.

ROTARY CONVERTER.

Specification of Letters Patent.

Patented Mar. 5, 1918.

Application filed July 6, 1915. Serial No. 88,120.

' To all whom it may concern:

Be it known that I, LEWIS W. CHUBB, a citizen of the United States, and a resident of Edgewood Park, in the county Allegheny and State of Pennsylvania, have invented,

a new and useful Improvement in Rotary Converters, of which the following is a specification.

My invention relates to rotary converters and to supply systems therefor, and it has for its object to provide means whereby the current neutralization and heat generation among the different armature conductors may be distributed and controlled in a simple and effective manner, resulting in a reduction of the average heatingthroughout the armature .winding, 9. reduction of the temperature of the hottest coils at a given load, or both of these results simultaneously, thus allowing an increase in the rating of the machine.

Referring to the accompanying drawings, Figure 1 is a diagrammatic view of arotary converter, together with a delta-diametrical supply system therefor, embodying an upper harmonic booster, illustrating one form of my invention; Fig. 2 is a view similar to that of Fig. l but shows a supply system of the star-diametrical type; Fig. 3 is a diagram illustratingthe partial graphic analysis of a square-top periodic wave; Fig. 4. is a diagram illustrating a possible method of current cancellation that may be employed in rotary converters in accordance with my invention; Fig. 5 is a diagram illustrating graphically the heating in an armature coil immediately behind an alternatingcurrent tap in an ordinary rotary converter operatin with a leading power factor of 95.7%; ig. 6 is a similar graphical illustration of the heat enerated 1n an armature coil immediately in advance of an alternating-current tap at a like power factor; Fig, 7 is a diagram showing the average heating throughout the various armature conductors in a rotary converter which does not embody my invention; Fig. 8 is a diagram similar to that of Fi 7 showing the average heating of the di erent armature coils in a rotary converter arranged in accordance with my invention for equal tap heating at difierent de ees of power factor; Figs. 9 and 1G. iagrams illustrating graphically the nil-nod in which I am enabled to e ualize the heating in armature coils'immediately in advance of and immeunitypower factor, a

diately behind the armature taps in a rotary converter operating at. 95.7% power factor by the use of circulatin third harmonic currents; Fig. 11.. is a dlagrammatic view of a twelve-phase rotary converter embodying my invention; and Fig. 12 is a dia gram showing graphically the improvement which may be effected in both the average and maximum heating of a twelve-phaserotary converter by the use of my invention.

In the ordinary rotary converter, if the effects of the converter losses are neglected and if the alternating-current supply is at square-top direct current wave of output and an alternating-current wave of input tend to flow in an armature coil midway between alternatin -current taps, the respective directions 0 flow opposing each other because of the fact that one is a driving and the other is a generated current. There is, therefore, a more or less perfect cancellation or neutralization of current in a mid coil. So long as current flow in a mid coil is considered, under the conditions assumed, the direct and alternatingcurrent waves are in phase with each other because the directcurrent wave necessarily reverses when passing under a brush and the alternating-current wave necessarily reverses at a point midway of the pole faces, which is also the brush position.

The extent of the current cancellation in the mid coil of a two-pole single-phase converter is shown graphically in Fig. 4 wherein a square-top wave 13l415-1617 1819 represents the direct current tending to flow, having an assumed maximum amplitude of 1, and the curve l320162119 represents a fundamental alternating-current input wave in phase therewith and having a maximum amplitude of 1.333. The net resultant current is shown by a curve 1314221517231819, all as is well known and understood in the art.

An inspection of Fig. 4 will show that the cancellation shown is the maximum attainable and that any phase displacement of the current waves with respect to each other in either direction will result in a greater net current and heating. Two factors cause such phase displacement, as follows: In any coil other than a mid coil, the alternatingcurrent wave is in phase with that in the mid coil, all turns between two alternatingcurrent taps being in series relation. On the other hand, the direct-current in any coil reverses when said coil passed under a brush, er, in other words, there is a small phase displacement between the square-top dlrectcmrent waves in each succeeding coil. As the alternating-current waves and the direst-current wave are in phase with each other for mid coil, it follows that they are out of phase to a greater and greater degree as one leaves the mid coil and approaches a tap coil, with resultant greater and greater heating. For a standard six-phase rotary, the increase'in heating, as one passes from mid coil to tap coil at unity power factor, is graphically shown in a curve 24b in Fig. 7, plotted in percentage of the heating as a direct-current generator.

Imperfect current cancellation is also influenced by the power factor of the alternating-current input. The electromotive force of the alternating input is in phase with the direct-current wave of the mid coil and, therefore, if the alternating-current wave is displaced with respect to its E. M. F. wave, a less efiectual cancellation will take place than is shown in Fig. 4 for the mid coil, and the influence will be marked on all the other coils, in one direction serving to neutralize the effect of displacement from mid position and in the other direction servin to accentuate the same feature. This is ilustrated in the curves 25 and 26 in Fig. 7 plotted for power factors of 95.7% and 85.6%, respectively, showing that, if the power factor is leading, a coil immediately behind an alternating-current tap has its current reduced and one immediately ahead of a tap has its current increased.

' Figs. 5 and 6 for t The relative magnitudes and phase relations of the various current waves of a standard si xphase rota converter are shown in e coils immediately following and immediately Eli-Seeding an alternating-current tap at a damental power factor of 95.7 %leading. In Fig. 5 a squaretop direct-current wave 35363738- 39-40, having anassumed amplitude of unity, is shown displaced from an alternating-current fundamental current wave 41- having a maximum amplitude of 1.333 by an angle of 3016 50'=13 l0, producing a net resultant current 45- 647-fl8-i950-51-52. By squaring the ordinates of the resultant curve, the heating curve 5354,5556'57-58 is obtained, the shaded area thereunder repre-, sentin the heat. The average height of the shad area is .246 indicating a resultant heating of 24.6% of that in the same coil when operating as a direct-current generator givin the same output.

In like manner in Fig. 6, wherein there is a displacement of 30+16 50=46 50, a heating curve is obtained which determines an area having an averageheight of .756 indicating that the heating in a coil immediately preceding an alternating-current tap is 75.6% of that when operated as a directcurrent generator.

Because of the fact that there is a more or less perfect cancellation of the input and output currents in a rotary converter, it is possible to operate a machine of this character with a much larger output for a given temperature rise than were it being driven as a direct-current generator. As above pointed out, the maximum heating occurs in the armature coils adjacent to the alternating-current taps which therefore, determine the safe operating load of the machine as a rotary converter. 1 An method, therefore, whereb the heating 0 the tap coils may be reduce even at the expense of increasing the heating in the mid coils, will allow a higher permissible rating in the machine and a consequent reduction in size and weight for a given output. The advantages to be gained bythe reduction in size and weight are such as to even justify an actual increase in the total average heating, provided said heating is more or less uniformly distributed throughout the winding.

By my invention, I produce circulating thirdeharmonic current waves in the electr1- cal circuits between the rotary converter and the secondary windings of its supply transformers, either by a s ecial triple frequency booster or by a suitable adjustment of the electrical constants of said electrical circuits. By suitably ad'usting the amplitude and phase of the circu ating third-harmonic current waves, I am enabled to reduce the tap-coil heating in a sixhase rotary co verter and, furthermore, 51c advanta of leading power factor may be obtaine with equal ta heating of a reasonable amount or I may, i desired, reduce the average heating without an increase in the ta -oo1l heating on unity power factor. Wit phase rotary converter, I am enabled to simultaneously reduce the tap-coil heat and the average heat throughout the armature windings b the proper selection and manipulation 0 upper-harmonic current waves.

The square-to direct-current wave tending to flow in t e armature conductor of a rotary converter is a constantly recurring periodic function and may therefore, be analyzed in accordance with Fouriers series into the sum of an infinite number of sine waves represented by the expression alent to the sum of a fundamental sine wave the twelverepresented by a line 1329-16-3019; and a residual wave sin 5124- sin 70 1 represented by a line 1314-31l5-16 17-32-18l9 and containing the fifth and all higher harmonics. The fundamental component sinli and, when evaluated, has a value 1.333 sin 0, as compared with the simultaneous instantaneous magnitude of the direct-current fundamental of 1.274 sin 6. It is there fore seen that there is an approximate cancellation between these two waves, the net difference being shown by a line 1333 163419 in Fig. 4. The remaining uncanceled portion of the direct-current wave is shown by a line 13142215--1723- 1819 in Fig. 4., bein the sum to infinity of the third and higher-harmonic components together with the uncanceled funlines 13-29163019.

damental current 1333 16-34-19. It ma be readily shown that the third and big er components, when squared, represent 18.9% of the heating of the mid coil when operating solely wit a direct-current wave as when driven as a direct-current enerator. The sum to infinity of the fi h and higher direct-current components, forming the line 1314-31--15l7-32-1819, when squared, amounts to but 9.9% of the direct-current heating. It is therefore ob vious that a radical reduction in mid coil n heating could be produced by establishing a circulation of third-harmonic current in the armature winding which would, at all times, have equal and opposite values to the triplefrequency. component represented by the As above pointed out, however, while this may be a highly advantageous procedure, in so far as the mid coils are concerned, the injection of a thirdharmonic current wave of the character described would exert a harmful influence in increasing the heating of the tap coils and, as the latter determine the rating'of the rotary converter, it is essential that some other phase relation of the third harmonics be chosen in order to obtain the desired results.

If the current in the mid coil is 1.333 sin 0=A, sin 0,

The direct current in any coil is Sill 30+; sin 50 3 0= 0 when the coil passes a brush.

The composite current is then i =%sin0+ "i=[(+A, cos 5) sinO +(A, sincos (n+5;- sin 30+ sin 56" (4) The heating in any coil is Q n n n v u o u u u a o o where .189 isthe aggregate heating of the third and higher-harmonics of the direct current. At the tap coil in a six-phase rotary,

The average heating will be Pasing now to the efi'ects of other than unitypower factor, the heat in any coil at an angle from the mid coilwith any value of circulating third-harmonic current is 2 Bti+ D,A cos 3-D,B, sin 3+.099 (7) where ED D355}, A, and B, are respectively the sine and cosine components of the fundamental, A and B are respectively the sine and cosine components of the third harmonic, and .099 is the aggregate heating of the fifth and higher armonics.

If r

[B -2D,B, I the taps will have equal heating, and for equal tap heating, the heating in any coil will be 2 A 213 13 D A B V b 5 3 +D,A, cos a +2D B S11).

from 1.833 may be obtained by flatting the voltage wave thereof with a sane component of third-harmonic voltage produced by the inductive drop of a pure cosine component of third-harmonic circulating current having a maximum amplitude dependent upon the inductance of the converter armature.

Applying these principles over the ordinary range of power factor, the following table may be computed, showing the desired phase and magnitude of circulating current the power factor being the fundamental power factor between the converter and the transformers and the true power factor in the line.

A, B, A; B; P. F.

on, cos 3-1),B, sin 3 +.099 8 shown, in Figs. 9 and 10, respectively, the conditions in the armature coils immediately following and immediately preceding an alternating-current tap in a six-phase rotary converter at a fundamental leading power factor of 95.7%, following, so far as possible, the arrangement and notation of Figs. 5 and 6. In each figure a pure cosine c0mponent of third-harmonic current 5960 616263-6465 is introduced, resulting in such modificationof the resultant current that the areas under the squared ordinate heating curves 5354-55565758 are equal, each having an average height of .575 indicating 57.5% of direct-current heating, in agreementwith the curve 25 in Fig. 8.

It will thus be seen that, by proper overexcitation to obtain 95.7% leading power factor, a radical im rovement in the line regulation may be e ected, and, at the same time, the machine may be operated at a more nearly constant coil temperature than would be possible under normal operating conditions, as shown in Figs. 6 and 7.

The circulating thirdharmonic currents exert-no influence on the external circuits in a delta-diametrically connected converting system. As shown in Fig. 1, a rotary converter 66 is rovided with an armature winding 67 and old poles 68 excited by any suitable means (not shown). Alternating current is supplied to the winding 6 through suitable ta and slip rings (not shown) from the -'ametrically connected secondary members 71, 73 and 75 of suitable supply transformers having primary members 72,74 and 76 deriving energy from mains 77. Direct current is removed the winding 67 through suitable brushes 78. Third-harmonic current waves are set up in the connections between the winding 67 and the secondary windings71, 7 3 and 75 by suitable adjustment of the electrical constants of said circuits or by a triple-frequency booster 79, of any desired construction, inserted in one of the leads. The third-harmonic current, at any instant, may be represented by arrows associated with the respective secondary windings. The currents induced thereby in the primary windings will assume the directions shown, tending to cause merely idle circulation in the delta of the primary windings.

The system of Fig. 2 is the same as that of Fig. 1 except that the transformers are arranged in a star-diametrical connection. \Vith this connection, a rotary converter may be used having a sine component of third-harmonic voltage in the diametral voltage wave shape which will flatten the diametral Voltage and contain an increased fundamental voltage, with resultant decreased fundamental current for the same brush voltage and load. -A decrease in the maximum value of the fundamental current from 1.333 to 1.274 will cause a perfect cancellation of the fundamental components of current in the mid coil. There will be a tap heating of 40.5% and an average heating of 25.88%. With afurther decrease of funda mental current to 1.163, the average heating is at its minimum value of 25.3%, and the taps have 39.3% heating. With 1.103 for.

fundamental current, the tap heating is reduced to a minimum of 39.1% and the average heating is 25.53%. or clearness, these results are tabulated as follows, together with the corresponding factors in directcurrent generator and standard rotary-converter operation.

Voltages. g'gfgfi g heating.

Remarks.

E,. E A,. A Top. Average.

1 0 0 0 100.00 100.00 AsD.C.genemtor. 1 0 1.833 0 41.82 26.79 Standard rotary. 1.06 .045 -1.274 0 40.54 26.88 heat in mid 001. 1.145 .145 --1.163 0 39.86 25.35 Min. average 1 heating. 1.200 .209 --1.10s 0 89.17 25.5: Kimtapheating.

The adjustment for minimum tap heating appears to be most favorable for operation, effecting a marked saving in the heating for a certain output or permitting an increase in the rating for a given tap heating.

The twelve-phase converter, shown diagrammatically in Fig. 11, with a two-phase third-harmonic booster in two adjacent taps thereof, was carefully investigated and it was found that improvement in the heating of all conductors could be obtained by the use of circulating third-harmonic currents. The ordinary twelve-phase converter has a tap-coil heatmgpf 25% of the heating when running as a C. generator, a mid-coil heating of 19.2%, and an average heating of 20.9%. This average heating can be lowered only as far as 20.7% by star-diametrical connection and a small third-harmonic voltage with no third-harmonic current circulating through the armature and the transformers. Under this condition, the tap coil will have 21.4% heating and the mid coil 11% heating, which is a great improvement over the standard tJVGIVGrPhfiSG converter and should be of commercial importance if the commutating problem for double capacity can be solved. Fig. 12 shows the heat diagram between successive taps of the standard and harmonic design of the twelvephase converter at unity power factor on the high side. At fundamental power fac tors lower than 100% there is also a decided advantage in the harmonic design, but the harmonic current, if used to best advantage, must be so shifted as to correct for the reac tive components of the fundamental current.

In a divisional application, Serial No. 184,246, filed August 3, 1917 and assigned to the Westinghouse Electric & Manufacturing.

invention to but a portion of the possible types of rotary converters but it will be obvious to -.those skilled in the art that the same the design of apparatus of the character indicated having various types of current supply systems and various numbers of operating phases.

I claim as my invention:

1. The combination with a rotary converter, of a source of alternating-current supply therefor, and means for producing current waves in the armature winding thereof having upper harmonic relation to the current waves of the alternating-current supply, said upper harmonic current waves having such a phase relation to the main supply waves as to equalize the heat. of the tap coils at a power factor other than unity with leading current.

2. The combination with a source of alternating current, of a rotary converter connected thereto, and means for developing a third harmonic of current in the armature winding of said rotary converter, said third harmonic having a phase displacement of ninety electrical degrees from the supply current.

3. The combination .with a source of alternating current, of a six-phase rotary conternating current, of a six-phase rotary congeneral principles maybe applied in.

verter connected thereto, and a third harmonic booster connected in one of the leads of said converter to develop third-harmonic current waves in the armature winding thereof, said harmonic waves having a phase displacement ofsubstantially ninety electrical degrees with respect to the main current waves from said source.

5. The combination with a six-phase rotary converter, of delta-diametrically connected transformers for supplying alternating current thereto, and a third harmonic booster connected in one of the leads from said transformers to the armature winding of said converter, said booster circulating current waves in the local circuits between said converter and said transformers, and said current waves havin triple frequency and substantially a ninety degree phase displacement with respect to the current waves of the main supply.

6. The combination with a rotary converter, of means for impressing upon the armature winding thereof a fundamental supply voltage of certain frequency and means for further impressing upon the armature winding thereof a cosine component of third-harmonic voltage in addition to said fundamental supply voltage, whereby the crest of said fundamental-voltage wave will be lowered and a more nearly perfect current cancellation in said armature winding will be efiected.

The method of operating a rota converter which comprises applying to the armature winding thereof alternating supply current of a certain frequency, over exciting the field windin to produce power factor other than unity with leading current, and further applying a cosine component of alternating current to said armature winding having a frequency which is an odd multiple of that of said supply current and of such magnitude as to equalize the heating in the tap coils. I

8. The method of operating a rota converter which comprises applying to t e armature winding thereof alternating supply current of a given normal frequency, overexciting the field windings thereof to produce power factor other than unity with leading current, and further applying auxiliary alternating current to said armature windin havin three times the frequency and suistantia y 90 phase displacement with respect to said" supply current and of such magnitude as to substantially equalize the heating in the tap coils.

In testimony whereof, I have hereunto subscribed my name this 26th day of June 60 LEWIS W, CHUBB. 

